Review: 1. 25 mL of 0.1 M barium hydroxide, Ba(OH)2, is added to 35 mL of 0.15 M hydrochloric acid, HCl. What is the pH of the resulting solution?

Review: 2. 30 mL of carbonic acid, H2CO3, is titrated to the equivalence point with 24.3 mL of 0.1 M sodium hydroxide, NaOH. What was the original concentration of the acid?

What is a Polyprotic Acid? In polyprotic acids, each ionizable proton dissociates in steps. Therefore in a titration, there are n equivalence points corresponding to each ionizable proton. For example in the titration of Na2CO3 with HCl, there are two equivalence points: One for the formation of HCO3 One for the formation of H2CO3

Titration Animation

Polyprotic Acid Titrations: Titration of H2C2O4 with NaOH Polyprotic Acid Titrations: Initial: H2C2O4 dissociating in water Buffering zone 1: H2C2O4 + OH-  1. Calculations rarely needed, concepts only!!! Equivalence point 1: All H2C2O4 and OH-1 reacted, only HC2O4- left 2. Polyprotic Acids are titrated “step-wise”, one proton at a time.

Polyprotic Acid Titrations: Buffering zone 2: HC2O4-1 begins to react with OH-1 Titration of H2C2O4 with NaOH Polyprotic Acid Titrations: Equivalence Point 2: All HC2O4-1 and OH-1 reacted, only C2O42- left 1. Calculations rarely needed, concepts only!!! 2. Polyprotic Acids are titrated “step-wise”, one proton at a time.

The initial sample of oxalic acid, before any titration Buffer Zone #1 Using the models provided on the handout, ID which represents the following points during the titration of H2C2O4. The initial sample of oxalic acid, before any titration Buffer Zone #1 Equivalence Point #1 Buffer Zone #2 Equivalence Point #2 Over-titration of the oxalic acid, too much base is added Spectator ions, water molecules, and very small amounts of H3O+ and OH- may be omitted

The oxalic acid has been over-titrated Spectator ions, water molecules, and very small amounts of H3O+ and OH- may be omitted

Buffer zone #1 Spectator ions, water molecules, and very small amounts of H3O+ and OH- may be omitted

Buffer zone #2 Spectator ions, water molecules, and very small amounts of H3O+ and OH- may be omitted

Equivalence Point #1 Spectator ions, water molecules, and very small amounts of H3O+ and OH- may be omitted

Equivalence Point #2 Spectator ions, water molecules, and very small amounts of H3O+ and OH- may be omitted

Initial sample of acid (no titration yet) Spectator ions, water molecules, and very small amounts of H3O+ and OH- may be omitted

Acids and Bases